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Dotted notation parser with pattern matching

Project description

Dotted

Sometimes you want to fetch data from a deeply nested data structure. Dotted notation helps you do that.

Let's say you have a dictionary containing a dictionary containing a list and you wish to fetch the ith value from that nested list.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}}
>>> dotted.get(d, 'hi.there[1]')
2

Grammar

Dotted notation looks similar to python. Both dot fields and slot fields, e.g. brackets, call __getitem__ internally. A dot field expects to see a dictionary-like object. A slot field is biased towards sequences (like lists, tuples, and strs) but can act on dicts as well. Dotted also supports slicing notation as well as transforms discussed below.

Patterns

You can use dotted for pattern matching. You can match to wildcards or regular expressions.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}, 'bye': {'there': [4, 5, 6]}}
>>> dotted.get(d, '*.there[2]')
(3, 6)
>>> dotted.get(d, '/h.*/.*')
([1, 2, 3],)

Dotted will return all values that match the pattern(s).

Slicing

Slicing is also supported. Dotted slicing works like python slicing and all that entails.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}, 'bye': {'there': [4, 5, 6]}}
>>> dotted.get(d, 'hi.there[::2]')
[1, 3]
>>> dotted.get(d, '*.there[1:]')
([2, 3], [5, 6])

The '+' operator

Both slots and slices support the '+' operator which refers to the end of sequence. You may append an item or slice to the end a sequence.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}, 'bye': {'there': [4, 5, 6]}}
>>> dotted.update(d, '*.there[+]', 8)
{'hi': {'there': [1, 2, 3, 8]}, 'bye': {'there': [4, 5, 6, 8]}}
>>> dotted.update(d, '*.there[+:]', [999])
{'hi': {'there': [1, 2, 3, 8, 999]}, 'bye': {'there': [4, 5, 6, 8, 999]}}

Transforms

You can optionally add transforms to the end of dotted notation. These will be applied on get and update. Transforms are separated by the | operator and multiple may be chained together. Transforms may be parameterized using the : operator.

>>> import dotted
>>> d = [1, '2', 3]
>>> dotted.get(d, '[1]')
'2'
>>> dotted.get(d, '[1]|int')
2
>>> dotted.get(d, '[0]|str:number=%d')
'number=1'

You may register new transforms via either register or the @transform decorator. Look at transforms.py for preregistered.

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